The proposed research concerns a study of certain purified toxins from venom of the scorpion, Centruroides sculpturatus, Ewing. These studies include (1) the effects upon the neuro-muscular junction of each of these toxins in both cholinergic and adrenergic transmission; (2) the immunological properties of the isolated toxins and the ability of antisera to one toxin to cross-react with the others; (3) the effects upon the biological properties of chemical alteration of amino acid side chains in these toxins.